In 1995, 84% of mortality in patients with CF was due to cardiopulmonary causes and the most common reason for hospitalization was an exacerbation of pulmonary disease. Good nutritional and growth status is associated with longer survival and with improvement or stabilization of pulmonary function in malnourished patients who have been renourished. We hypothesize that children with better energy balance as indicated by height and weight z-scores and will have better pulmonary function as indicated by FEV1. A sample of 90, 6 to 8 year old children with CF and pancreatic insufficiency from four CF centers will be randomized into two groups. One group will receive a comprehensive nutrition enhancement program so as to achieve and maintain optimal growth and body composition. The other group will receive usual care based upon each Centers' current practices, and will likely have growth patterns similar to the general population of CF children. Subjects will be assessed over two years (baseline, 6, 12, 18, and 24 months) for measurements of pulmonary function, nutritional status, energy balance, food intake, and disease severity.